This invention relates to a method and apparatus for cooling materials by a fluid spray process, and is particularly applicable for cooling hot materials formed by an extrusion process.
In the manufacture of products made of metal, glass, ceramics, or plastics e.g., it is often necessary to cool the product at a controlled rate in order to obtain desired properties of strength, ductility, or surface appearance. Several methods for cooling steel for example, are described in "Quenching of Steel" ASM Committee Publication, H. J. Bates, Chairman, Metals Handbook, Vol. 2, ASM (1976). The described cooling methods include use of a water bath, high speed water jets, air, and charged and uncharged water mists. However, all of these suffer from one or more limitations or disadvantages.
In the water bath method, the surface heat transfer rate is limited by the vapor that is trapped between the material surface and the liquid. Also, material shapes of non-uniform thickness are often distorted due to uneven cooling rates. Further, the water in the bath must be frequently cleaned.
In the high speed water jet method, closely spaced jets are used to penetrate the trapped vapor between the blanket of water and the hot surface. However, distortion due to uneven cooling is a problem especially for material having thin or non-uniform shapes. Moreover, large quantities of water must be cleaned, chemically treated, and recirculated.
The air cooling method is frequently used to cool thin or non-uniform shapes slowly in order to avoid distortion of the material. However, this method requires a large floor space.
When cooling an object with an uncharged mist, droplets of water are suspended in air. While this method is faster than air cooling alone and reduces floor space, it is inefficient because most of the water drops drift away without being evaporated. When using a charged water mist to cool hot materials, a larger percentage of the water drops reach the object due to electrostatic attraction. However, some water drops still drift away without evaporating.
In summary, the above-described methods result in distortion of the material because of non-uniform cooling, have a slow cooling rate, require the use of large quantities of cooling fluid, are inefficient, and/or require the use of a large space or working area.